Abstract: An apparatus for add/drop multiplexing of a wavelength channel multiplex comprises an MMI coupler and MI arm section. The MMI coupler includes a multiplex input, an add channel input, a drop channel output, a multiplex output, and at least four input/output terminals. The MI arm section includes four waveguides, wherein each waveguide is optically connected to a respective one of said input/output terminals of the MMI coupler; and is at least provided with a first phase control element, a reflection grating, a second phase control element, and a wide frequency range reflection means. Further, each of the reflection gratings are provided with a heater means for tuning the respective reflection grating to the wavelength channel to be added/dropped and the wide frequency range reflection means reflect all other channels.